1. Field of the Invention
The present invention relates to a motor control system for controlling a servomotor for driving an axis of a driving mechanism of an industrial machine such as a robot, a machine tool, an injection molding machine and a press machine.
2. Description of Related Art
In an industrial machine such as a robot, a machine tool, an injection molding machine and a press machine, a driving axis for driving a driven member is driven by a servomotor such that a position and/or a velocity of the driving axis is feedback controlled by position control processing and velocity control processing. Conventionally, operation constants, such as gains, for use in mathematical operations in the position control processing and the velocity control processing have been set to fixed values. The position control processing and/or the velocity control processing is performed using the fixed operation constants even in a control system where stability of the system varies in dependence on a position of the driving axis (a position of the driven member and a rotational position of the servomotor).
For example, in a machine in which a nonlinear element is intervened between the servomotor and the driven member in a transmission mechanism for mechanically connecting the servomotor and the driven member such that relation of a rotational position of the servomotor with respect to a position of the driven member is not proportional, a ratio between the position feedback and the velocity feedback changes in dependence of the position of the driving axis. Since this is equivalent to an effect that a reduction ratio of the transmission mechanism dynamically changes in accordance with the position of the driven member, the control system becomes stable at a position of a relatively large reduction ratio and unstable at a position of a relatively small reduction ratio. Thus, in the conventional motor control system, the operation constants have been predetermined in view of the stability of the system at the position where the dynamic reduction ratio of the transmission mechanism is relatively small. As a result, the operation at the position where the dynamic reduction ratio is relative large to be made slow to delay the whole cycle time of motion of the machine.